1. Field of the Invention
This invention relates to the field of mechanical connectors, and in particular to connector assemblies for stage separation systems, such as satellite and missile systems.
2. Description of Related Art
Transport systems, such as rockets that transport satellites into space, vessels that transport submerged sections of ocean structures such as oil platforms, and the like, require a means for securely fastening different items together for transport, and reliably and easily unfastening the items for deployment. Multi-stage rockets also require a means for fastening the stages together, and reliably unfastening the stages as each stage is spent. In other situations, such as aircraft carrier based aircraft, the items are transported or stored in a disassembled state and require a means for rapidly fastening the items for deployment, and reliably and easily unfastening the items for subsequent storage or transport.
A variety of devices have been developed to secure two items together while also allowing the items to be separated quickly and reliably. In the aerospace industry, the common connection devices include bolts and bands that can be severed. Bolts are used to fasten the two items together, and an explosive charge is typically used to sever the bolts at the proper time, thereby unfastening the two items. Depending upon the application, ancillary devices such as springs may be used to urge the two items apart when the bolts are severed. To assure a reliable separation, the number of bolts used to fasten the two items is kept to a minimum; this results in load points at the bolts far in excess of the load imposed by a distributed fastening system.
Belt structures are commonly used to provide for a distributed load. A belt structure that is commonly employed to fasten items together is a "V-band", typified by U.S. Pat. No. 4,715,565, incorporated by reference herein. The V-band includes a tension belt for securing a plurality of retainers against camming surfaces on flange members on separable spacecraft component parts.
A typical V-band embodiment consists of an upper ring attached to the payload, a lower ring attached to the launch vehicle, and a clampband that is circumferentially tensioned to the flanges of the upper and lower rings, as illustrated in FIG. 1. The upper ring 101 and lower ring 102 each have flanges that, when joined, form a "V" shaped projection 150A. The clampband consists of a belt 110 and a plurality of clamps 120. Each of the clamps 120 have a recess 150B corresponding to the shape of the projection 150A of the upper 101 and lower 102 rings. When the belt 110 is tensioned, the recesses 150B of the clamps 120 are compressed against the projections 150A, thereby securing the upper 101 and lower 102 rings together.
The belt 110 is conventionally tensioned by bolts (not shown) that are in line with the belt 110, and explosive bolt cutters are used to sever the bolts to release the tension. When the tension in the belt 110 is released, the clamps 120 are free to separate from the projection 150A, thereby decoupling the upper 101 and lower 102 rings. The conventional V band structure also includes means, such as springs, for urging the clamps 120 apart from the projection 150A, to provide for a reliable separation. Means are also provided to retain the belt 110 and clamps 120 after separation, to minimize the occurrence of "space junk".
For V-bands to work properly, the tension required in the tensioning belt 110 is relatively high (about 3800 pounds for a 38 inch diameter; 6800 pounds for a 66 inch diameter). This high tension requires radial stiffeners in the rings 101, 102. The sudden release of this stored energy generates high shock, and imposes additional requirements on the means used to retain the fast moving belt and clamps after separation. Because of the high tension requirements, the combined weight of the belt, clamps, and ancillary required devices is substantial (as much as 25 pounds for a 38 inch diameter V-band structure). The high tension requirements of V-bands often require specialized tools and instruments to tension the band. The high tension and high release shock effects also limits the reliable life of the components, thereby limiting the amount of testing that can be applied to the components that are actually flown.
Another structure that is commonly used to provide for an easily separable connection is an explosive frangible joint, as typified by U.S. Pat. Nos. 4,685,376 and 5,390,606. An explosive detonating cord is placed within a contained space that forms the frangible joint between the two items. Separation is achieved by detonating the cord within the contained space, forcing a rapid crack propagation through the frangible joint. Although the weight of an explosive frangible joint is less than that of an equivalent sized V-band, it is still substantial (as much as 17 pounds for a 38 inch diameter joint). The destructive nature of this separation system precludes testing of the joints that are actually flown.
Each of the aforementioned separation connectors also imparts a substantial shock to the connected items upon separation, and the explosive nature of the devices used for separation introduce a risk of personal injury, particularly during pre-launch assembly and testing. Because of the shock effects, such separation connectors are not commonly used on items that are routinely disassembled for storage or transport.